A gear is general means for transmitting drive force, but gear noise (noise or vibration) is generated in some cases when gears are in mesh with each other.
Conventionally, to solve the problem mentioned above, a crowning process is generally performed on a tooth surface of a gear. The crowning process is processing by which crowning bulging in an arc shape is formed along a tooth trace direction on the tooth surface of the gear. The crowning process described above can be achieved by applying machining in such a way that a tooth thickness is gradually reduced from a central portion in the tooth trace direction to both end portions in the tooth trace direction. Since the meshing of the gears is made smooth by performing the crowning process as described above, the gear noise can be reduced.
In addition, when crowning is applied to the gear subjected to heat treatment, the crowning process is generally performed at the same time as grinding. In the grinding, a grinding wheel is moved in an arc in such a way as to follow the shape of the crowning, and the arc movement of the grinding wheel is enabled by adjusting a center distance between the gear and the grinding wheel according to the crowning shape. For example, Patent Document 1 discloses a gear grinding method in which crowning is applied to the tooth surface of the gear as described above.